Purification of arylamines



l atentecl Sept. 15, 1931 UNITED STATES PATENT oF ic ilEDGAR C. BRITTON,OF MIDLAND, IQIICHIGAN ASSIGNOR T DOW CHEMICAL COM- PANY, 0F MIDLAND,MICHIGAN, CORPORATION OF MICHIGAN PURIFICATION OF ARYLAMINES No Drawing.

In the method of making a primary arylamine wherein a mono-halogenatedaromatic hydrocarbon is reacted with aqueous amp monia solution at anelevated temperature and pressure and in the presence of a coppercompound as catalyst, the resulting reaction product separates uponstanding into an aqueous layer containing chiefly ammonia, ammoniumchloride and copper salt in solu- 1 tion, and an oily layer consistingchiefly of the primary arylamine product and a lesser amount of thecorresponding phenolic compound, together with relatively small amountsof the corresponding secondary aminc, diarylether and other compounds.The

oil layer also contains traces of water, ammonium salt and coppercompounds. Such oil layer is separated from the aqueous layer andtreated for the purification of the primary arylamine product. Thelatter procedure involves numerous practical diificulties, arisingprincipally from the persistency with which the phenolic compoundfrequently accompanies the primary arylamine through the variouspurification'steps.

For example in the manufacture of aniline by reacting betweenchlorbenzene and aqueous ammonia solution with a cuprous compound ascatalyst, the oil layer so obtained contains, in addition to aniline,from 3 to 8 per cent of phenol, along with smaller amounts ofdiphenylamine, diphenyl oxide, copper and ammonia compounds. 'Inpurifying this product the complete separation of phenol presentsconsiderable diliiculty.

The formation of such phenol is unavoidably connected with the aforesaidprocess, being due to the hydrolytic action of water present. \Vhile inpractice hydrolysis is 40 largely restrained by providing a large excessof ammonia, nevertheless a certain condition of equilibrium between thereacting components exists, such that a definite modicum of phenol isalways produced. A procedure for elfecting a substantially quantitativeseparation of such phenol from the aniline is essential for obtaining apure waterwhite product that is permanent and will remain for a longperiod without material discoloration. To the accomplishment of theApplication filed February 15, 1929. Serial No. 340,336.

foregoing and related ends the invention, then, consists of the stepshereinafter fully described and particularly pointed out in the claims,the following description setting forth in detail certain procedurewhereby the principle of the invention may be used.

As previously stated, the reaction mixture derived from theaforementioned process for the manufacture of an arylamine, e. g.aniline, separates upon standing into an aqueous and an oily layer, theformer containing excess ammonia, and soluble ammonia and coppercompounds together with small amounts. of aniline and phenol insolution, while the latter consists of the bulk of the crude anilineproduct together with unreacted chlorbenzone and organic impurities suchas phenol, diphenylamine, diphenyl oxide, etc., as well as traces ofammonia and copper compounds. On boiling the aqueous layer the anilineand phenol content thereof is steamed out, collected by suitable meansand added tothe oily layer.

The oily layer is treated with barium hydrate in quantity suflicient toneutralize and fix the phenol, as barium phenate, break up the ammoniacompounds and precipitate the copper compounds. Such barium hydrate maybe added either as crystals approximately of compositon Ba(OH) .8H O, oras an aqueous solution thereof. The -mixture is thereupon distilled,conveniently at atmospheric pressure, to drive oif,,first, ammonia andthen all of the water. A small amount of chlorbenzene and aniline iscarried over with the steam and is recovered from the distillate, beingreturned either to the initial reaction or to the main body of crudeaniline remaining in the still, depending upon the proportions ofchlorbenzene and aniline contained therein.

I have found that barium phenate may be heated in the presence of Waterat boiling temperature without materially undergoing hydrolysis ordecomposition. This behavior distinguishes the barium phenate from thecorresponding calcium compound, the latter being strongly hydrolyzedunder the conditions as just described. Accordingly, if one attempted todistill the water out of a mixture of aniline, water and calciumphenate, the latter compound would be more or less completely hydrolyzedby the water present and phenol would be reformed, thus defeating thepurpose of the operation.

After distilling off water as just described the crude anilineisobtained in a substantially anhydrous condition, the phenol contentthereof being present as dry barium phenate. The mixture is nowdistilled, preferably under reduced pressure, e, g. about 23 to 27inches vacuum. The first fraction coming over contains the chlorbenzene,this being returned to the original reaction. Pure aniline then distillsover as a clea-r'water-white product. WVhen distillation is completed aheavy, semi-solid residue is left in the still, such residue containingbarium phenate, diphenylamine, diphenyl oxide, copper compounds andtarry decomposition products.

T t is then added to the still t d s ll? h, P e end e queen mixture istilled to drive off small amounts of residual aniline retained therein,the latter being slightly impure so that after recovery it is preferablyadded to a succeeding charge of crude aniline to the st ll. The sti lconten s are then drained off and f ltered to separate the insolublesludge from the clear solution of barium phenate. The sludge containingcopper compounds may be returned to the original reaction for thepurpose of supplying Pe of the npron compo nd ataly t therein T Phene eso ution may be a-oic t d to lib rat fre phenol, the la t r bei g p edand pu ifi d in the u ua ay, h le th a iu c mpound may e cover d and, ifdesired, converted to the hydrate for u e in he process h efl oaoy o t ef r going method for p i y g e eruc e niline p oduct and sep ng t fr m,ac ompanying phe ol is bee e to' least in ge part in ran m ng n l phenolinto n'metnllie phenate substantially non-hydrolyzed under theconditions of operation, thereby permitting complete separation of waterfrom the crude material Without material decomposition or hydrolysistakingplace therein. Enamples of such relatively non-hydrolyzed metallicp na s ar he ph nates o the al li metals and barium. On the other handcalcium phenate, for example, is readily hydroyZe l n he pre en e o Wer, ence the present procedure cannot be employed therewith. After thepreliminary separation of ater a d fix n. of p eno t e anili e productmay be distilled from the anhydrous mixture and recovered in a state ofexceptional purity, the purified product being ark dly su erior to thather for bta nable by ot er methods,- Fur he mo residual aw mate ls andy-p dno re covered,v loss s o the lues con ained. th e n b ing almost ngl gible,

the method herein disclosed, provided the step orsteps stated b'y 'anyof the following aims or the equivalent of such stated t p or steps'beemployed;

I refore part c arly po nt ut and disin tly c aim as my inv ntion,

In a m thod, o puri ying the or d ryiamnie prod ct of a reacti n etweena halogenated aromatic hydrocarbon and aqueous ammonia solution, saidproduct also, tenung a r lativ ly small amount of e phenolic compound,the Steps which consist in treating sald crude product With barium ydrae in amount u f ci nt to conv sai phenolic compound to. phenate,removing ater herefrom by distillat on and then t l g said. erylaininefrom the resulti g anhydrous mixture,

2. In a method of. pur ying t e crude aniline product of a reactionbetween chlorenzen a d qu ous ammonia so ution, said product alsocontaining a relatively small mount o phen l, the steps hich con ist inating a d c ude p oduct with bari m yd e i amoun sufiicien to. con ertsaid phenol o phenat removing Water the efr m y ation} and then distiling se rl @1111- line r the esu ting an yd ous mintn e- 3- The m thod ofseparating an arylami e nd a e a ely all amou t.- of a. ph nol dm xturetogether w ich mprise reat- 1 ing the mixture with* barium", hydrate inmount s fl e to, conr rt s ch. phenol to ip enate, IQIIl-OF-Tlfl' waterthere r m by istill ttiou, andthen distilling said arylamine om theresult ng anhydrous. mixture.

e method of s p rating ani in a d a a rela ively mell a oun o phenol inadxture to ether which comprises. treatmg the mixture. with bariumhydrate in amount suflicient to convert such phenol to phena te,

removing Water h r f o by d stillation, nd then dis il ng sai an l nerom the resulting anhydrous mixture.

Signed by me this 5 day o eh, 1,92

' EDGA C. BRITTON.

